<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        div.father{
            width: 1288px;
            height: 40px;
            background-color: darkgray;
        }
        div.son{
            width: 800px;
            height: 35px;
            padding: 5px 0 0 10px;
            background-color: orange;
            /*margin-left: auto;*/
            /*margin-right: auto;*/
            margin: 0 auto;
        }
    </style>
</head>
<body>
<div class="father">
    <div class="son">
        你好
    </div>
</div>
</body>
</html>